1. Field of the Invention
This invention relates to a method for transmitting a signal in HDBn code combined with an auxiliary binary signal on a digital transmission medium. The auxiliary signal has a lower bit-rate than the bit-rate of the HDBn code signal. The HDBn code signal comprises four predetermined and different sequences each having (n+1) successive elements whose (n-1) central elements are zeros and whose last element is a bipolarity violation mark.
More particularly, the invention concerns such a method specially adapted to the monitoring of pairs of repeaters in a bidirectional digital transmission line between a monitoring end equipment and a monitored end equipment.
2. Description of the Prior Art
The majority of known repeater monitoring systems involve a frequency combination of the information signal whose in-line code is an HDBn code, and of one or more binary remote locate signals which modulate a low-frequency subcarrier with a frequency decidedly lower than that of the information signal. The end equipments and repeaters in these systems comprise, associated with each of two channels of the line, separating and combining filters for the low-frequency remote locate auxiliary signals transmitted from the monitoring equipment or low-frequency auxiliary signals representative of repeater error rates and transmitted from the repeaters with the respective information signal toward the monitoring equipment. The filters consists of transformers and shock coils which have the drawback of being heavy and cumbersome. Additionally, the use of such filters prevents high ratios between the information signal bit-rate and the auxiliary signal bit-rate. This results in restricting any remote monitoring of high bit-rate digital information signals using low-frequency auxiliary signals; this bit-rate is becoming much more common-place in digital transmission trunks between multistage multiplexers-demultiplexers.